Victor Hugo Benioff

NATIONAL ACADEMY OF SCIENCES V ICTOR HUGO BENIOFF 1899—1968 A Biographical Memoir by F R A N K P RESS Any opinions expressed in this memoir are those of the author(s) and do not necessarily reflect the views of the National Academy of Sciences. Biographical Memoir COPYRIGHT 1973 NATIONAL ACADEMY OF SCIENCES WASHINGTON D.C. VICTOR HUGO BENIOFF September 14,1899-February 29,1968 BY FRANK PRESS ICTOR HUGO BENIOFF was born on September 14, 1899, in VLos Angeles, California. His parents were both immigrants —his father from Russia and his mother from Sweden. Ben- ioff's California roots and his origins from immigrant stock were reflected in later years in his love of nature and his sensitivity to people, particularly his sympathy for the underdog. Benioff was drawn to science at an early age, expressing a career interest in astronomy as a boy of fourteen. He attended public schools in Los Angeles and Long Beach and took his undergraduate studies at Pomona College, where he was elected to Phi Beta Kappa in 1920 and received the A.B. degree in 1921. During his undergraduate years he served as a summer assistant working on solar astronomy at the Mount Wilson Observatory, returning to Mount Wilson each summer until his graduation from Pomona. His interest in astronomy continued following graduation and he took a position at the Lick Ob- servatory for the year 1923-1924, observing stellar radial veloc- ities. Were it not for his inability to tolerate the night hours and the cold, as required of an observer, Benioff would un- doubtedly have become an eminent astronomer. In 1924 he began work in Pasadena as an assistant physicist with the seismological program of the Carnegie Institution, 28 BIOGRAPHICAL MEMOIRS then directed by H. O. Wood. His first assignment was to de- velop a drive system for the recording drums. Even at this early date Benioff's taste for sophisticated instrumental design was evidenced. By developing a new type of impulse motor driven from a fork-controlled 10 Hertz quarter-phase pulse generator, he solved the problem. This novel system was highly successful and made possible the determination of seismic- wave arrival times to the unprecedented accuracy of 0.1 second. At about this time Benioff installed most of the original instrumentation and set up a number of the original auxil- iary stations which subsequently evolved into the famous seismic network of the California Institute of Technology. Circa 1929 he commenced design of the now world-famous variable reluctance seismograph and the linear strain seismograph. The former instrument was placed in service in 1931 and evolved to its final form in 1934. For a number of reasons, the variable reluctance seismograph was an immediate success; capable of extremely high magnification at a frequency of about 1 Hertz, it was useful for the study of near and distant earthquakes. Simplicity, reliability, sensitivity, and a judicious se- lection of response characteristics based upon the noise and signal spectrums are responsible for the adoption of this re- markable instrument by observatories all over the world. It made possible the precise determination of travel time, the discovery of new seismic phases, the extension of the magnitude scale to teleseismic events, and the world-wide availability of first-motion data to recover source mechanism. With minor modification this instrument was later selected for use in the World-Wide Standard Seismograph Network and formed the basis of the detection system recommended by the Geneva Con- ference of Experts for the monitoring of nuclear tests. The original strain seismograph was built with water pipe and lacked the desired stability. Gradually it evolved over the VICTOR HUGO BENIOFF 29 years with fused quartz tubing used as the standard of length, velocity transducers with galvanometric recording, and finally variable capacitance transducers and recording oscillographs. This instrument achieved notable successes; in 1953 Benioff provided linear strain records to Frank Press and Maurice Ewing and thereby made possible the discovery of the mantle surface waves. The linear strain seismograph is now a primary source of data for the eigen-frequency spectrum of the earth. Beginning about 1934, Benioff supervised the development of instruments for structural vibration studies in a program sponsored by the U.S. Coast and Geodetic Survey. This was followed in 1936 by a number of instrumental advances de- signed to improve the quality of the (Pasadena) Southern California seismograph stations, making them the most ad- vanced network in the world. A number of resulting devices were manufactured commercially and placed in world-wide use. During this period Benioff also developed instruments for seismic prospecting—a field of rapid technological advances, keen competition, and overnight obsolescence. In these and sub- sequent instrumental developments Benioff led an enthusias- tic staff of engineers and technicians, many of whom became well known in seismological circles: Francis Lehner, Ralph Gilman, J. L. Blayney, and William Giles. Benioff received the Ph.D. degree from the California In- stitute of Technology in 1935. The Seismological Laboratory was transferred from the Carnegie Institution to Caltech in 1937 and Benioff was appointed assistant professor of seismology. In 1950 he was promoted to a full professorship at Caltech. Although he would have made an excellent instructor, Ben- ioff preferred research to teaching and had little contact with students either in the classroom or as thesis adviser. On the other hand, his influence via informal discussion with doctoral candidates, postdoctoral fellows, and visiting scholars was very 30 BIOGRAPHICAL MEMOIRS great and more than justified the title "professor." By the mid-thirties the Seismological Laboratory of Pasadena became a world center for geophysical research owing to the originality and productivity of Benioff and his close colleagues, Beno Gut- enberg and Charles Richter. With the increasing concern for national defense connected with the outbreak of World War II in Europe, Benioff and his group undertook the development and improvement of radar and underwater listening and ranging devices mostly for the Submarine Signal Company of Boston. This work continued through the war years and terminated in 1946. Following the war Benioff returned to geophysical research. He built an array of seismometers on Mount Palomar to study microseisms. He experimented with new types of seismograph systems involving novel concepts such as mixing strain seismograph outputs to obtain mode filtering, vectorial recording devices, mercury tube tiltmeters, tape recording and playback analysis of earthquakes. About 1957, Benioff became interested in magnetic micropulsations. He constructed an array of mag- netovariographs and published one of the first papers—and still perhaps the most comprehensive—on the spectrum of geo- magnetic fluctuations in the range 0.3 to 120 seconds. Still widely used is Benioff's early definition of seismic de- structiveness in which the acceleration spectrum is the im- portant parameter in anti-seismic design. This was one mani- festation of a special responsibility Benioff felt to the inhabitants of earthquake prone regions. Benioff's curiosity was unbounded. In addition to geophysical instrumentation, he took an active interest in the fabrication of a super-lightweight bicycle and construction of exotic kites; he studied camera lenses in great detail and even delved into the workings of jet engines. The use of ultrasonic devices for cancer treatment also attracted his attention. He became in- VICTOR HUGO BENIOFF 31 tensely interested in the physics of musical instruments and worked toward the development of an electronic violin, cello, and piano. The last instrument reached fruition under spon- sorship of the Baldwin Piano Company and was used in public concerts by famous artists. His motivation always was to heighten the pleasure of the listener and to lighten the task of the performer while preserving the fidelity of the instrument. Benioff's instruments and the data which they produced were sufficient ingredients for a distinguished scientific career, However, his interests broadened, and beginning about 1950 he began working on the general problem of earthquake mech- anisms and global tectonics—some fifteen years prior to the current great interest in this field. In a classic series of papers between 1951 and 1958 he introduced several of the concepts which today form the basic elements of the "new global tectonics." In attacking these problems he made good use of his broad knowledge of the engineering properties of materials. By nature he was inclined toward elegantly simple hypotheses and quantitative procedures. His approach was that of a mature scientist entering a dormant field; he was skeptical, bold, and unfettered by preexisting hypotheses. During this period Benioff introduced the concept of in- strumentally determined strain rebound. He was able to show that great earthquakes reveal a global pattern of strain ac- cumulation and release. He outlined the relation between after- shock sequences and stress relaxation and showed that the strain rebound characteristics could be used to separate the crust and upper mantle into zones having different mechanical properties. Benioff demonstrated that the geographic distribution of aftershocks was related to the dimension of the primary fault. He proposed that the distribution of epicenters could

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